Electronic device including housing and flexible display panel

ABSTRACT

An electronic device includes a housing and a display panel. The housing includes a flat surface, a first side surface including a curved surface, second and third side surfaces adjacent to the first side surface and including a curved surface, and a fourth side surface opposite to the first side surface and including a curved surface. The display panel includes a first region overlapping with the flat surface, a second region overlapping with the first side surface and including a curved surface, a third region overlapping with the second side surface and including a curved surface, and a fourth region overlapping with the third side surface and including a curved surface.

TECHNICAL FIELD

The present invention relates to an object, a method, or a manufacturingmethod. In addition, the present invention relates to a process, amachine, manufacture, or a composition of matter. In particular, oneembodiment of the present invention relates to a light-emitting device,a display device, an electronic device, a lighting device, a drivingmethod thereof, or a manufacturing method thereof. In particular, oneembodiment of the present invention relates to a display panel (displaydevice) capable of display on a curved surface. One embodiment of thepresent invention relates to an electronic device, a light-emittingdevice, or a lighting device that includes a display device capable ofdisplay on a curved surface, or a manufacturing method thereof.

BACKGROUND ART

Recent display devices are expected to be applied to a variety of usesand become diversified. For example, reduction in thickness, improvementin performance, and multi-functionalization of a portable informationterminal such as a smartphone or a tablet terminal including a touchpanel have progressed.

Patent Document 1 discloses a flexible active matrix light-emittingdevice in which an organic EL element and a transistor serving as aswitching element are provided over a film substrate.

REFERENCE Patent Document

[Patent Document 1] Japanese Published Patent Application No.2003-174153

DISCLOSURE OF INVENTION

An object of one embodiment of the present invention is to provide anovel electronic device. Another object of one embodiment of the presentinvention is to provide an electronic device capable of a variety ofdisplay. Another object of one embodiment of the present invention is toprovide an electronic device which can be operated in a variety of ways.Another object of one embodiment of the present invention is to providea display device (display panel) which can be used for such anelectronic device. Another object of one embodiment of the presentinvention is to provide a novel display device.

Note that the descriptions of these objects do not disturb the existenceof other objects. Note that in one embodiment of the present invention,there is no need to achieve all the objects. Objects other than theabove objects will be apparent from and can be derived from thedescription of the specification and the like.

One embodiment of the present invention is a display panel whichincludes a flexible substrate, a first display region, a second displayregion, and a third display region. The first display region has aquadrangle outline and includes a first side and a second side forming afirst corner portion of the outline. The second display region is incontact with the first side and the width of the second display regionin a direction parallel to the first side coincides with the length ofthe first side. The third display region is in contact with the secondside and the width of the third display region in a direction parallelto the second side coincides with the length of the second side. Thesubstrate has a notch portion in a region facing the first displayregion with the first corner portion provided therebetween.

It is preferable that the display panel include a plurality of pixelsand the pixels each include a transistor including an oxidesemiconductor in a semiconductor layer in which a channel is formed.

It is preferable that the display panel include a plurality of pixelsand the pixels each include a transistor including polycrystallinesilicon in a semiconductor layer in which a channel is formed.

It is preferable that the display panel further include a first drivercircuit which outputs a signal to the first display region and thesecond display region and a second driver circuit which outputs a signalto the third display region. It is preferable that the first drivercircuit be provided along a side of the second display region which isopposite to the first side, and the second driver circuit be providedalong a side of the third display region in a direction in which thefirst side extends. The first driver circuit and the second drivercircuit are preferably electrically connected to each other through awiring.

Alternatively, It is preferable that the display panel further include adriver circuit which outputs a signal to the first display region, thesecond display region, and the third display region. It is preferablethat the driver circuit be provided along a side of the second displayregion which is opposite to the first side and the driver circuit andthe third display region be electrically connected to each other througha wiring.

A fourth display region in contact with a third side of the firstdisplay region which is opposite to the first side is preferablyprovided.

A fourth display region in contact with a third side of the firstdisplay region which is opposite to the first side and a fifth displayregion in contact with a fourth side of the first display region whichis opposite to the second side are preferably provided.

Another embodiment of the present invention is an electronic deviceincluding any one of the above display panels and a housing. The housinghas a top surface, a rear surface, a first side surface, a second sidesurface in contact with the first side surface, a third side surfaceopposite to the first side surface, and a fourth side surface oppositeto the second side surface. Each of the first side surface and thesecond side surface preferably has a curved surface continuous from thetop surface to the rear surface. It is preferable that the first displayregion of the display panel be provided along the top surface, thesecond display region thereof be provided along the first side surface,and the third display region thereof be provided along the second sidesurface.

Another embodiment of the present invention is an electronic deviceincluding the above display panel and a housing. The housing has a topsurface, a rear surface, a first side surface, a second side surface incontact with the first side surface, a third side surface opposite tothe first side surface, and a fourth side surface opposite to the secondside surface. Each of the first side surface, the second side surface,and the third side surface preferably has a curved surface continuousfrom the top surface to the rear surface. It is preferable that thefirst display region of the display panel be provided along the topsurface, the second display region thereof be provided along the firstside surface, the third display region thereof be provided along thesecond side surface, and the fourth display region thereof be providedalong the third side surface.

Another embodiment of the present invention is an electronic deviceincluding the above display panel and a housing. The housing has a topsurface, a rear surface, a first side surface, a second side surface incontact with the first side surface, a third side surface opposite tothe first side surface, and a fourth side surface opposite to the secondside surface. Each of the first side surface, the second side surface,the third side surface, and the fourth side surface preferably has acurved surface continuous from the top surface to the rear surface. Itis preferable that the first display region of the display panel beprovided along the top surface, the second display region thereof beprovided along the first side surface, the third display region thereofbe provided along the second side surface, the fourth display regionthereof be provided along the third side surface, and the fifth displayregion thereof be provided along the fourth side surface.

Any one of the above electronic devices is preferably further providedwith a touch sensor at a position overlapping with the display panel,and the touch sensor is preferably provided along the top surface and atleast one of the first side surface, the second side surface, the thirdside surface, and the fourth side surface of the housing.

Note that in this specification, the display device might include any ofthe following modules in its category: a module in which a connectorsuch as a flexible printed circuit (FPC) or a tape carrier package (TCP)is attached to a display panel (display device); a module having a TCPprovided with a printed wiring board at the end thereof; and a modulehaving an integrated circuit (IC) directly mounted by a chip on glass(COG) method over a substrate over which a display element is formed.

According to one embodiment of the present invention, a novel electronicdevice can be provided. Alternatively, an electronic device capable of avariety of display can be provided. Alternatively, an electronic devicewhich can be operated in a variety of ways can be provided.Alternatively, a display device which can be used for such an electronicdevice can be provided. Alternatively, a novel display device can beprovided.

Note that the description of these effects does not disturb theexistence of other effects. One embodiment of the present invention doesnot necessarily achieve all the objects listed above. Other effects willbe apparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B illustrate a structure example of an electronic deviceof an embodiment;

FIGS. 2A 1, 2A2, 2B 1, and 2B2 illustrate structure examples of anelectronic device of an embodiment;

FIGS. 3A1, 3A2, 3B1, and 3B2 illustrate structure examples of anelectronic device of an embodiment;

FIG. 4 illustrates a structure example of an electronic device of anembodiment;

FIGS. 5A and 5B illustrate a structure example of an electronic deviceof an embodiment;

FIGS. 6A to 6C illustrate structure examples of a display panel of anembodiment;

FIGS. 7A and 7B illustrate structure examples of a display panel of anembodiment;

FIGS. 8A to 8C illustrate a structure example of a display panel and atouch sensor of an embodiment;

FIGS. 9A to 9C illustrate a structure example of a display panel of anembodiment;

FIGS. 10A to 10C illustrate structure examples of a display panel of anembodiment;

FIGS. 11A to 11C illustrate structure examples of a display panel of anembodiment;

FIGS. 12A to 12D are Cs-corrected high-resolution TEM images of a crosssection of a CAAC-OS and a cross-sectional schematic view of theCAAC-OS;

FIGS. 13A to 13D are Cs-corrected high-resolution TEM images of a planeof a CAAC-OS;

FIGS. 14A to 14C show structure analysis of a CAAC-OS and a singlecrystal oxide semiconductor by XRD;

FIGS. 15A and 15B show electron diffraction patterns of a CAAC-OS;

FIG. 16 shows a change of crystal parts of an In—Ga—Zn oxide owing toelectron irradiation;

FIGS. 17A and 17B illustrate a structure example of an electronic deviceof an embodiment;

FIGS. 18A and 18B illustrate a structure example of an electronic deviceof an embodiment;

FIGS. 19A1, 19A2, 19B1, and 19B2 illustrate structure examples of anelectronic device of an embodiment;

FIGS. 20A1, 20A2, 20B1, and 20B2 illustrate structure examples of anelectronic device of an embodiment; and

FIGS. 21A1, 21A2, 21B1, and 21B2 illustrate structure examples of anelectronic device of an embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments will be described in detail with reference to drawings. Notethat the present invention is not limited to the description below, andit is easily understood by those skilled in the art that various changesand modifications can be made without departing from the spirit andscope of the present invention. Accordingly, the present inventionshould not be interpreted as being limited to the content of theembodiments below.

Note that in the structures of the invention described below, the sameportions or portions having similar functions are denoted by the samereference numerals in different drawings, and description of suchportions is not repeated. Furthermore, the same hatching pattern isapplied to portions having similar functions, and the portions are notespecially denoted by reference numerals in some cases.

Note that in each drawing described in this specification, the size, thelayer thickness, or the region of each component is exaggerated forclarity in some cases. Therefore, embodiments of the present inventionare not necessarily limited to such a scale.

Note that in this specification and the like, ordinal numbers such as“first”, “second”, and the like are used in order to avoid confusionamong components and do not limit the number.

Embodiment 1

In this embodiment, an electronic device of one embodiment of thepresent invention and a display panel (also referred to as a displaydevice) which can be used in the electronic device are described withreference to drawings.

[Examples of Electronic Device]

FIG. 1A is a schematic perspective view illustrating the top surfaceside of an electronic device described below, and FIG. 1B is a schematicperspective view illustrating the rear surface side thereof.

The electronic device illustrated in FIGS. 1A and 1B includes a housing101 and a display panel 110 which is provided on a surface of thehousing 101.

The housing 101 has a top surface, a rear surface, a first side surface,a second side surface in contact with the first side surface, a thirdside surface opposite to the first side surface, and a fourth sidesurface opposite to the second side surface.

The display panel 110 includes a first display region 111 overlappingwith the top surface of the housing 101, a second display region 112overlapping with one of the side surfaces of the housing 101, and athird display region 113 overlapping with another one of the sidesurfaces of the housing 101. Here, suppose that the first side surfaceof the housing 101 overlaps with the second display region 112 and thesecond side surface of the housing 101 overlaps with the third displayregion 113.

Among the four side surfaces of the housing 101, at least a regionoverlapping with the display panel 110 preferably has a curved surface.For example, it is preferable that there be no corner portion betweenthe top surface and the side surface and between the side surface andthe rear surface, and that these surfaces are continuous. Furthermore,the side surface is preferably a curved surface such that theinclination of a tangent line is continuous from the top surface to therear surface of the housing 101. In particular, the side surfacepreferably has a developable surface that is obtained by transforming aflat surface without expansion and contraction.

As illustrated in FIGS. 1A and 1B, the second display region 112 isprovided along the first side surface of the housing 101 and may extendto the rear surface of the housing 101. The third display region 113 isprovided along the second side surface of the housing 101 and may extendto the rear surface of the housing 101. Alternatively, a structureillustrated in FIGS. 17A and 17B may be employed. FIG. 17A is aschematic perspective view illustrating the top surface side of anelectronic device, and FIG. 17B is a schematic perspective viewillustrating the rear surface side thereof. Alternatively, a structureillustrated in FIGS. 18A and 18B may be employed. FIG. 18A is aschematic perspective view illustrating the top surface side of anelectronic device, and FIG. 18B is a schematic perspective viewillustrating the rear surface side thereof.

In addition to the display panel 110, a hardware button, an externalconnection terminal, or the like may be provided on the surface of thehousing 101.

Although FIGS. 1A and 1B show the case where the two side surfaces ofthe housing 101 are used as the display region, the display region mayoverlap with another side surface.

FIGS. 2A1 and 2A2 illustrate a structure where a fourth display region114 overlaps with the third side surface of the housing 101 which isopposite to the first side surface. FIGS. 2B1 and 2B2 illustrate astructure where a fifth display region 115 overlapping with the fourthside surface of the housing 101 which is opposite to the second sidesurface is provided in addition to this. Alternatively, a structureillustrated in FIGS. 19A1 and 19A2 may be employed. FIG. 19A1 is aschematic perspective view illustrating the top surface side of anelectronic device, and FIG. 19A2 is a schematic perspective viewillustrating the rear surface side thereof. Alternatively, a structureillustrated in FIGS. 19B1 and 19B2 may be employed. FIG. 19B1 is aschematic perspective view illustrating the top surface side of anelectronic device, and FIG. 19B2 is a schematic perspective viewillustrating the rear surface side thereof. Alternatively, a structureillustrated in FIGS. 20A1 and 20A2 may be employed. FIG. 20A1 is aschematic perspective view illustrating the top surface side of anelectronic device, and FIG. 20A2 is a schematic perspective viewillustrating the rear surface side thereof. Alternatively, a structureillustrated in FIGS. 20B1 and 20B2 may be employed. FIG. 2081 is aschematic perspective view illustrating the top surface side of anelectronic device, and FIG. 20B2 is a schematic perspective viewillustrating the rear surface side thereof.

FIGS. 3A 1 and 3A2 illustrate a structure where the second displayregion 112 overlapping with the first side surface of the housing 101and the fourth display region 114 overlapping with the third sidesurface of the housing 101 which is opposite to the first side surfaceare provided. FIGS. 3B 1 and 3B2 illustrate a structure where only thethird display region 113 overlapping with the second side surface of thehousing 101 is provided. Alternatively, a structure illustrated in FIGS.21A1 and 21A2 may be employed. FIG. 21 A1 is a schematic perspectiveview illustrating the top surface side of an electronic device, and FIG.21A2 is a schematic perspective view illustrating the rear surface sidethereof. Alternatively, a structure illustrated in FIGS. 21B 1 and 21 B2may be employed. FIG. 21B 1 is a schematic perspective view illustratingthe top surface side of an electronic device, and FIG. 21B2 is aschematic perspective view illustrating the rear surface side thereof.

With such a structure, display can be performed not only on a surfaceparallel to the top surface of a housing, as in conventional electronicdevices, but also on a surface parallel to a side surface of thehousing. In particular, a display region is preferably provided alongtwo or more side surfaces of the housing because the variety of displayis further increased.

The first display region 111 provided along the top surface of thehousing 101 and the display regions provided along the side surfaces ofthe housing 101 may be independently used as display regions to displaydifferent images and the like, or two or more of the display regions maydisplay one image or the like. For example, a continuous image may bedisplayed on the first display region 111 provided along the top surfaceof the housing 101, the second display region 112 provided along theside surface of the housing 101, or the like.

FIG. 4 shows an example of a use state of the electronic deviceillustrated in FIGS. 2A1 and 2A2. In FIG. 4, text data 122, a pluralityof icons 121 associated with an application or the like, and the likeare displayed on the first display region 111 provided along the topsurface of the housing 101. Icons 123 associated with an application orthe like, and the like are displayed on the second display region 112provided along the first side surface of the housing 101.

Furthermore, as illustrated in FIG. 4, display can be performed so thattext data 124 or the like rolls (moves) across a plurality of displayregions (here, the third display region 113 and the second displayregion 112) provided along the side surfaces of the housing 101. Byperforming display across two or more surfaces of the housing in thismanner, a user can be prevented from missing displayed data regardlessof the direction of the electronic device when, for example, a phonecall is received.

In addition, transmitter information (e.g., a name, a phone number, ane-mail address, and the like of a transmitter) may be displayed on notonly the first display region 11 but also a display region providedalong the side surface such as the second display region 112 when, forexample, a phone call or an e-mail is received. FIG. 4 shows an exampleof the case where transmitter information is displayed to roll acrossthe second display region 112 and the third display region 113 when ane-mail is received.

FIGS. 5A and 5B show an example of a use state of an electronic devicedifferent from the above. In FIG. 5A, the plurality of icons 121 aredisplayed on the first display region 111 and a slide bar 125 isdisplayed on the second display region 112. By touching the slide bar125 with a finger 126 or the like to move the slide bar up or down,display contents such as the icons 121 displayed on the first displayregion 111 are slid up or down accordingly as illustrated in FIG. 5B.FIGS. 5A and 5B illustrate a state where images of the plurality oficons 121 and the like are slid up from the first display region 111 tothe third display region 113 by sliding the slide bar 125 down with thefinger 126.

Although the case where an image displayed on the first display region111 is an icon is shown here, one embodiment of the present invention isnot limited thereto; depending on a launched application, a variety ofdata such as text, still images, and moving images can be displayed andslid. The position of the slide bar 125 is not limited to the seconddisplay region 112, and the slide bar 125 may be provided on the firstdisplay region 11, the third display region 113, the fourth displayregion 114, or the like.

During a standby time during which the electronic device is not used,display on the first display region 111 provided along the top surfaceof the housing 101 may be turned off (e.g., black display) and data maybe displayed only on the second display region 112 or the like providedalong the side surface. Display on the first display region 111 havingan area larger than those of the other display regions is not performed,so that power consumption in a standby time can be reduced.

It is preferable that a touch sensor be provided at a positionoverlapping with the display panel 110, specifically, in regionsoverlapping with the display regions. As the touch sensor, a sheet-likecapacitive touch sensor may be provided to overlap with the displaypanel 110. Alternatively, a so-called in-cell touch panel that has atouch sensor function may be provided as the display panel 110 itself.For the in-cell touch panel, a capacitive touch sensor may be used or anoptical touch sensor using a photoelectric conversion element may beused.

For example, in the structure illustrated in FIG. 4, combination oftouch operations on the first display region 111, the second displayregion 112, the third display region 113, and the fourth display region114 is preferably associated with an application operation.

An example of association between combination of touch operations on thesecond display region 112, the third display region 113, and the fourthdisplay region 114 and an application operation is shown in thefollowing table. For example, a power on/off operation is performed whenall the three display regions are touched. When the second displayregion 112 and the fourth display region 114 are touched at the sametime, an application associated with an e-mail is started and contentsof the e-mail are displayed at the same time. When the second displayregion 112 and the third display region 113 are touched at the sametime, an application for making a phone call is started. When the thirddisplay region 113 and the fourth display region 114 are touched at thesame time, a browser is started.

TABLE 1 Touch operation Second display Third display Fourth displayregion region region Operation touched touched touched power on/offtouched not touched touched open e-mail touched touched not touched makephone call not touched touched touched start browser

The above association between the touch operation and the application isan example, and it is preferable that a developer of operating system orapplication software or a user can determine an association asappropriate.

Alternatively, application operations are performed by touching one ormore of the second to fourth display regions in a state where the firstdisplay region 111 is touched, in which case an unintended operation canbe less likely to be started.

By associating combination of touch operations on a plurality of regionswith application operations as described above, an intuitive operationis possible; thus, a user-friendly human interface can be obtained.

An electronic device of one embodiment of the present invention canperform display along not only the top surface but also two or more sidesurfaces of the housing; thus, display can be performed in various waysas compared with a conventional electronic device. Furthermore, a touchsensor is provided in each of the display regions; thus, variousoperations can be performed as compared with a conventional electronicdevice and an electronic device capable of a more intuitive operationcan be obtained.

Note that an example of the case where a variety of display is performedusing the display panel 110 is shown here; however, one embodiment ofthe present invention is not limited thereto. For example, depending oncircumstances or conditions, data is not necessarily displayed. As anexample, the electronic device may be used as a lighting device, not thedisplay panel 110. By using the device as a lighting device, it can beused as interior lighting having an attractive design. Alternatively, itcan be used as lighting with which various directions can beilluminated. Further alternatively, it may be used as a light source,e.g., a backlight or a front light, not the display panel 110. In otherwords, it may be used as a lighting device for the display panel.

[Structure Example of Display Panel]

Next, a structure example of a display panel which can be used for theelectronic device of one embodiment of the present invention isdescribed with reference to drawings.

FIG. 6A is a schematic top view of the display panel 110 describedbelow. The display panel 110 includes a flexible substrate 102 and aplurality of pixels over the substrate 102. The display panel 110includes the first display region 111, the second display region 112,the third display region 113, and the fourth display region 114. Notethat different hatching patterns of display regions are used here forclarification.

The outline of the first display region 111 is a quadrangle. The seconddisplay region 112 is provided in contact with one (a first side 131) offour sides forming the outline of the first display region 111. Thewidth of the first display region 111 preferably coincides with that ofthe second display region 112 in a direction parallel to the first side131. The third display region 113 is provided in contact with a secondside 132 which is in contact with the first side 131. The width of thefirst display region 111 preferably coincides with that of the thirddisplay region 113 in a direction parallel to the second side 132.Furthermore, a corner portion (first corner portion) formed by the firstside 131 and the second side 132 preferably meets one of corner portionsof the second display region 112 and one of corner portions of the thirddisplay region 113.

As illustrated in FIG. 6A, the substrate 102 includes a notch portion138 in a region facing the first display region 111 with the firstcorner portion formed by the first side 131 and the second side 132provided therebetween. Owing to the notch portion 138, the seconddisplay region 112 and the third display region 113 can be bent indifferent directions.

FIG. 6A illustrates a structure in which the fourth display region 114is provided in contact with a third side 133 opposite to the first side131. One of corner portions of the fourth display region 114 preferablymeets a second corner portion formed by the second side 132 and thethird side 133. The substrate 102 includes a notch portion similar tothe notch portion 138 in a region facing the first display region 111with the second corner portion provided therebetween. With such astructure, the fourth display region 114 and the third display region113 can be bent in different directions.

Part of the substrate 102 is provided with an FPC 103 which supplies asignal and electric power for driving the pixels. Although FIG. 6Aillustrates a structure in which an IC 104 is mounted on the FPC 103 bya COF method, the IC 104 is not necessarily provided. The IC 104 may bedirectly mounted on the substrate 102 by a COF method. Here, the widthof the FPC 103 is preferably smaller than that of the first displayregion 111. Thus, particularly in the case where the second displayregion 112 and the fourth display region 114 are bent and the firstdisplay region 111 is flat, a junction portion of the FPC 103 and thesubstrate 102 is not bent and therefore, the FPC 103 can be preventedfrom being peeled.

FIG. 6B is a schematic top view in which a region A in FIG. 6A isenlarged.

In FIG. 6B, a first driver circuit 141 which outputs a signal fordriving pixels included in the first display region 111 and the seconddisplay region 112 to the first display region 111 and the seconddisplay region 112 and a second driver circuit 142 which outputs asignal for driving pixels included in the third display region 113 tothe third display region 113 are provided. The first driver circuit 141is provided along a side of the second display region 112 which isopposite to the first side 131. The second driver circuit 142 isprovided along a side of the third display region 113 which is a side ina direction in which the first side 131 extends. The first drivercircuit 141 and the second driver circuit 142 are electrically connectedto each other through a wiring 145, and a signal input from the FPC 103can be supplied to the second driver circuit 142 through the wiring 145.

FIG. 6C illustrates a structure different from that in FIG. 6B. In FIG.6C, a driver circuit 143 is provided instead of the first driver circuit141. The driver circuit 143 can output a signal for driving pixelsincluded in the first display region 111 and the second display region112 and a signal for driving pixels included in the third display region113. The signals output from the driver circuit 143 can be output towirings electrically connected to the pixels in the third display region113, through wirings 146.

As each of the first driver circuit 141, the second driver circuit 142,and the driver circuit 143, for example, a circuit serving as a gatedriver circuit or a source driver circuit can be used; preferably, agate driver circuit is used. In this case, the IC 104 preferably has afunction as a source driver circuit.

Although a so-called driver integrated type display panel including adriver circuit over the substrate 102 is described here, a drivercircuit is not necessarily provided over the substrate 102.

As described above, the second driver circuit 142 which outputs a signalfor driving the pixels included in the third display region 113 or thewirings 146 which supplies a signal for driving the pixels is providedalong the side of the third display region 113; thus, the area of thenotch portion 138 can be increased and the area of a non-display portionwith respect to a surface area of the display panel 110 can be reduced.In the case where the third display region 113 is bent as illustrated inFIGS. 5A and 5B, a structure in which a driver circuit is not providedin a bent portion as illustrated in FIG. 6C is preferable. Sinceelectrical characteristics of a semiconductor element such as atransistor in a driver circuit might be changed owing to stress causedby bending, instability of an output signal from the driver circuit canbe prevented with such a structure.

Although FIGS. 6A to 6C illustrate the structure in which the first tofourth display regions are provided, first to third display regions maybe provided or the fifth display region 115 may be additionallyprovided. FIG. 7A is a schematic top view showing the case where thefifth display region 115 is provided. A wiring between the fifth displayregion 115 and the second display region 112 and a driver circuit mayhave structures similar to those in FIG. 6B or FIG. 6C.

Furthermore, FIG. 7B illustrates an example of a structure where an FPC103 a is provided. The FPC 103 a has a function of supplying a signaland electric power to, for example, the driver circuits described above.In the case where the display panel 110 does not include a drivercircuit, an IC may be mounted on the FPC 103 a by a COF method or thelike.

Here, an oxide semiconductor is preferably used for semiconductordevices such as transistors used for pixels included in display regionsor driver circuits in the display panel 110. In particular, an oxidesemiconductor having a wider band gap than silicon is preferably used. Asemiconductor material having a wider band gap and a lower carrierdensity than silicon is preferably used because off-state current of thetransistor can be reduced.

The oxide semiconductor preferably contains at least indium (In) or zinc(Zn), for example. More preferably, the oxide semiconductor contains anoxide represented by an In-M-Zn-based oxide (M is a metal such as Al,Ti, Ga, Ge, Y, Zr, Sn, La, Ce, or Hf).

As the semiconductor layer, it is preferable to use an oxidesemiconductor film including a plurality of crystal parts whose c-axesare aligned perpendicular to a surface on which the oxide semiconductorfilm is formed or the top surface of the oxide semiconductor film and inwhich the adjacent crystal parts have no grain boundary.

There is no grain boundary in such an oxide semiconductor; therefore,generation of a crack in an oxide semiconductor film which is caused bystress when a display panel is bent is prevented. Therefore, such anoxide semiconductor can be preferably used for a flexible display panelwhich is used in a bent state, or the like.

The use of such materials for the semiconductor layer makes it possibleto provide a highly reliable transistor in which a change in theelectrical characteristics is suppressed.

Charge accumulated in a capacitor through a transistor can be held for along time because of the low off-state current of the transistor. Whensuch a transistor is used for a pixel, a driver circuit can be stoppedwhile a gray scale of an image displayed on each display region ismaintained. As a result, an electronic device with an extremely lowpower consumption can be obtained.

Note that details of a preferable mode and a formation method of anoxide semiconductor that can be used for the semiconductor layer aredescribed in an embodiment below.

Alternatively, a polycrystalline semiconductor may be used forsemiconductor devices such as transistors used for pixels included indisplay regions or driver circuits in the display panel 110. Forexample, polycrystalline silicon or the like is preferably used.Polycrystalline silicon can be formed at a lower temperature than singlecrystal silicon and has higher field effect mobility and higherreliability than amorphous silicon. When such a polycrystallinesemiconductor is used for a pixel, the aperture ratio of the pixel canbe improved. Even in the case where pixels are provided at extremelyhigh resolution, a gate driver circuit and a source driver circuit canbe formed over a substrate over which the pixels are formed, and thenumber of components of an electronic device can be reduced.

Here, FIGS. 8A to 8C illustrate an example where a sheet-like touchsensor is provided to overlap with the display panel 110.

FIG. 8A illustrates a state where part of the display panel 110 providedwith the FPC 103 is bent. FIG. 8B illustrates a state where a sheet-liketouch sensor 105 is bent in accordance with a curved surface of thedisplay panel 110. The touch sensor 105 is provided with an FPC 106.

FIG. 8C illustrates a state where the display panel 110 and the touchsensor 105 are overlapped with each other. Here, as illustrated in FIG.8C, it is preferable that the FPC 103 provided for the display panel 110and the FPC 106 provided for the touch sensor 105 not overlap with eachother. Therefore, the display panel 110 and the touch sensor 105preferably do not have the same shape, and in a region to which the FPC103 or the FPC 106 is attached, the display panel 110 and the touchsensor 105 preferably have different shapes so as not to overlap witheach other.

As described above, the display panel 110 and the sheet-like touchsensor 105 are overlapped with each other and incorporated in thehousing 101; thus, a touch function can be added to not only the topsurface but also part of a side surface and the rear surface of thehousing.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Embodiment 2

In this embodiment, a structure of a touch panel that can be used in anelectronic device of one embodiment of the present invention will bedescribed with reference to FIGS. 9A to 9C.

FIG. 9A is a top view illustrating a structure of a touch panel that canbe used in an electronic device of one embodiment of the presentinvention.

FIG. 9B is a cross-sectional view taken along line A-B and line C-D inFIG. 9A.

FIG. 9C is a cross-sectional view taken along line E-F in FIG. 9A.

<Top View>

A touch panel 300 described as an example in this embodiment includes adisplay portion 301 (see FIG. 9A).

The display portion 301 includes a plurality of pixels 302 and aplurality of imaging pixels 308. The imaging pixels 308 can sense atouch of a finger or the like on the display portion 301. Thus, a touchsensor can be formed using the imaging pixels 308.

Each of the pixels 302 includes a plurality of sub-pixels (e.g., asub-pixel 302R). In addition, in the sub-pixels, light-emitting elementsand pixel circuits that can supply electric power for driving thelight-emitting elements are provided.

The pixel circuits are electrically connected to wirings through whichselection signals are supplied and wirings through which image signalsare supplied.

Furthermore, the touch panel 300 is provided with a scan line drivercircuit 303 g(1) that can supply selection signals to the pixels 302 andan image signal line driver circuit 303 s(1) that can supply imagesignals to the pixels 302.

The imaging pixels 308 include photoelectric conversion elements andimaging pixel circuits that drive the photoelectric conversion elements.

The imaging pixel circuits are electrically connected to wirings throughwhich control signals are supplied and wirings through which powersupply potentials are supplied.

Examples of the control signals include a signal for selecting animaging pixel circuit from which a recorded imaging signal is read, asignal for initializing an imaging pixel circuit, and a signal fordetermining the time it takes for an imaging pixel circuit to detectlight.

The touch panel 300 is provided with an imaging pixel driver circuit 303g(2) that can supply control signals to the imaging pixels 308 and animaging signal line driver circuit 303 s(2) that reads out imagingsignals.

<Cross-Sectional View>

The touch panel 300 includes a substrate 310 and a counter substrate 370that faces the substrate 310 (see FIG. 9B).

The substrate 310 is a stacked body in which a flexible substrate 310 b,a barrier film 310 a that prevents diffusion of unintentional impuritiesto the light-emitting elements, and an adhesive layer 310 c thatattaches the barrier film 310 a to the substrate 310 b are stacked.

The counter substrate 370 is a stacked body including a flexiblesubstrate 370 b, a barrier film 370 a that prevents diffusion ofunintentional impurities to the light-emitting elements, and an adhesivelayer 370 c that attaches the barrier film 370 a to the substrate 370 b(see FIG. 9B).

A sealant 360 attaches the counter substrate 370 to the substrate 310.The sealant 360 also serving as an optical adhesive layer has arefractive index higher than that of air. The pixel circuits and thelight-emitting elements (e.g., a light-emitting element 350R) areprovided between the substrate 310 and the counter substrate 370.

<<Structure of Pixel>>

Each of the pixels 302 includes the sub-pixel 302R, a sub-pixel 302G,and a sub-pixel 302B (see FIG. 9C). The sub-pixel 302R includes alight-emitting module 380R, the sub-pixel 302G includes a light-emittingmodule 380G, and the sub-pixel 302B includes a light-emitting module380B.

For example, the sub-pixel 302R includes the light-emitting element 350Rand the pixel circuit that can supply electric power to thelight-emitting element 350R and includes a transistor 302 t (see FIG.9B). Furthermore, the light-emitting module 380R includes thelight-emitting element 350R and an optical element (e.g., a coloringlayer 367R).

The light-emitting element 350R includes a lower electrode 3511R, anupper electrode 352, and a layer 353 containing a light-emitting organiccompound between the lower electrode 351R and the upper electrode 352(see FIG. 9C).

The layer 353 containing a light-emitting organic compound includes alight-emitting unit 353 a, a light-emitting unit 353 b, and anintermediate layer 354 between the light-emitting units 353 a and 353 b.

The light-emitting module 380R includes the coloring layer 367R on thecounter substrate 370. The coloring layer transmits light of aparticular wavelength and is, for example, a layer that selectivelytransmits light of red, green, or blue color. Note that a region thattransmits light emitted from the light-emitting element as it is may beprovided as well.

The light-emitting module 380R, for example, includes the sealant 360that is in contact with the light-emitting element 350R and the coloringlayer 367R.

The coloring layer 367R is positioned in a region overlapping with thelight-emitting element 350R. Accordingly, part of light emitted from thelight-emitting element 350R passes through the sealant 360 that alsoserves as an optical adhesive layer and through the coloring layer 367Rand is emitted to the outside of the light-emitting module 380R asindicated by arrows in FIGS. 9B and 9C.

Note that although the case where the light-emitting element is used asa display element is described here, one embodiment of the presentinvention is not limited thereto.

For example, in this specification and the like, a display element, adisplay device which is a device including a display element, alight-emitting element, and a light-emitting device which is a deviceincluding a light-emitting element can employ a variety of modes or caninclude a variety of elements. Examples of a display element, a displaydevice, a light-emitting element, or a light-emitting device include anEL (electroluminescent) element (e.g., an EL element including organicand inorganic materials, an organic EL element, or an inorganic ELelement), an LED (e.g., a white LED, a red LED, a green LED, or a blueLED), a transistor (a transistor which emits light depending oncurrent), an electron emitter, a liquid crystal element, electronic ink,an electrophoretic element, a grating light valve (GLV), a plasmadisplay panel (PDP), a micro electro mechanical system (MEMS), a digitalmicromirror device (DMD), a digital micro shutter (DMS), MIRASOL(registered trademark), an interferometric modulator display (IMOD)element, an electmwetting element, a piezoelectric ceramic display, or acarbon nanotube, which are display media whose contrast, luminance,reflectivity, transmittance, or the like is changed by electromagneticaction. Examples of display devices having EL elements include an ELdisplay. Examples of a display device including an electron emitterinclude a field emission display (FED), and an SED-type flat paneldisplay (SED: surface-conduction electron-emitter display). Examples ofdisplay devices including liquid crystal elements include a liquidcrystal display (e.g., a transmissive liquid crystal display, atransflective liquid crystal display, a reflective liquid crystaldisplay, a direct-view liquid crystal display, or a projection liquidcrystal display). Display devices having electronic ink orelectrophoretic elements include electronic paper and the like.

<<Structure of Touch Panel>>

The touch panel 300 includes a light-blocking layer 367BM on the countersubstrate 370. The light-blocking layer 367BM is provided so as tosurround the coloring layer (e.g., the coloring layer 367R).

The touch panel 300 includes an anti-reflective layer 367 p positionedin a region overlapping with the display portion 301. As theanti-reflective layer 367 p, a circular polarizing plate can be used,for example.

The touch panel 300 includes an insulating film 321. The insulating film321 covers the transistor 302 t. Note that the insulating film 321 canbe used as a layer for planarizing unevenness caused by the pixelcircuits. An insulating film on which a layer that can prevent diffusionof impurities to the transistor 302 t and the like is stacked can beused as the insulating film 321.

The touch panel 300 includes the light-emitting elements (e.g., thelight-emitting element 350R) over the insulating film 321.

The touch panel 300 includes, over the insulating film 321, a partition328 that overlaps with an end portion of the lower electrode 351R (seeFIG. 9C). In addition, a spacer 329 that controls the distance betweenthe substrate 310 and the counter substrate 370 is provided on thepartition 328.

<<Structure of Image Signal Line Driver Circuit>>

The image signal line driver circuit 303 s(1) includes a transistor 303t and a capacitor 303 c. Note that the driver circuit can be formed inthe same process and over the same substrate as those of the pixelcircuits. As illustrated in FIG. 9B, the transistor 303 t may include asecond gate over the insulating film 321. The second gate may beelectrically connected to a gate of the transistor 303 t, or differentpotentials may be supplied thereto. The second gate may be provided in atransistor 308 t described below, the transistor 302 t, or the like ifnecessary.

<<Structure of Imaging Pixel>>

The imaging pixels 308 each include a photoelectric conversion element308 p and an imaging pixel circuit for sensing light received by thephotoelectric conversion element 308 p. The imaging pixel circuitincludes the transistor 308 t.

For example, a PIN photodiode can be used as the photoelectricconversion element 308 p.

<<Other Structures>>

The touch panel 300 includes a wiring 311 through which a signal can besupplied. The wiring 311 is provided with a terminal 319. Note that anFPC 309(1) through which a signal such as an image signal or asynchronization signal can be supplied is electrically connected to theterminal 319.

Note that a printed wiring board (PWB) may be attached to the FPC309(1).

Transistors formed in the same process can be used as the transistor 302t, the transistor 303 t, the transistor 308 t, and the like.

Transistors of a bottom-gate type, a top-gate type, or the like can beused.

As a gate, source, and drain of a transistor, and a wiring or anelectrode included in a touch panel, a single-layer structure or astacked structure using any of metals such as aluminum, titanium,chromium, nickel, copper, yttrium, zirconium, molybdenum, silver,tantalum, and tungsten, or an alloy containing any of these metals asits main component can be used. For example, a single-layer structure ofan aluminum film containing silicon, a two-layer structure in which analuminum film is stacked over a titanium film, a two-layer structure inwhich an aluminum film is stacked over a tungsten film, a two-layerstructure in which a copper film is stacked over acopper-magnesium-aluminum alloy film, a two-layer structure in which acopper film is stacked over a titanium film, a two-layer structure inwhich a copper film is stacked over a tungsten film, a three-layerstructure in which a titanium film or a titanium nitride film, analuminum film or a copper film, and a titanium film or a titaniumnitride film are stacked in this order, a three-layer structure in whicha molybdenum film or a molybdenum nitride film, an aluminum film or acopper film, and a molybdenum film or a molybdenum nitride film arestacked in this order, and the like can be given. Note that atransparent conductive material containing indium oxide, tin oxide, orzinc oxide may be used. Copper containing manganese is preferably usedbecause controllability of a shape by etching is increased.

The above-described oxide semiconductor is preferably used as asemiconductor in which a channel of a transistor such as the transistor302 t, the transistor 303 t, or the transistor 308 t is formed. Detailsof a preferable mode of the oxide semiconductor are described in anembodiment below.

Alternatively, silicon may be used as a semiconductor in which a channelof a transistor such as the transistor 302 t, the transistor 303 t, orthe transistor 308 t is formed. Although amorphous silicon may be usedas silicon, silicon having crystallinity is particularly preferable. Forexample, microcrystalline silicon, polycrystalline silicon, singlecrystal silicon, or the like is preferably used. In particular,polycrystalline silicon can be formed at a lower temperature than singlecrystal silicon and has higher field effect mobility and higherreliability than amorphous silicon. When such a polycrystallinesemiconductor is used for a pixel, the aperture ratio of the pixel canbe improved. Even in the case where pixels are included at extremelyhigh definition, a gate driver circuit and a source driver circuit canbe formed over a substrate over which the pixels are formed, the numberof components included in an electronic device can be reduced.

Here, a method for forming a flexible display panel is described.

Here, a structure including a pixel and a driver circuit or a structureincluding an optical member such as a color filter is referred to as anelement layer for convenience. An element layer includes a displayelement, for example, and may include a wiring electrically connected toa display element or an element such as a transistor used in a pixel ora circuit in addition to the display element.

Here, a support provided with an insulating surface over which anelement layer is formed is called a base material.

As a method for forming an element layer over a base material providedwith an insulating surface having flexibility, there are a method inwhich an element layer is formed directly over a base material, and amethod in which an element layer is formed over a supporting basematerial having stiffness unlike a base material, and then the elementlayer is separated from the supporting base material and transferred tothe base material.

In the case where a material of the base material can withstand heatingtemperature in the process for forming the element layer, it ispreferable that the element layer be formed directly over the basematerial, in which case a manufacturing process can be simplified. Atthis time, the element layer is preferably formed in a state where thebase material is fixed to the supporting base material, in which casetransfer of the element layer in a device and between devices can beeasy.

In the case of employing the method in which the element layer is formedover the supporting base material and then transferred to the basematerial, first, a separation layer and an insulating layer are stackedover a supporting base material, and then the element layer is formedover the insulating layer. Then, the element layer is separated from thesupporting base material and then transferred to the base material. Atthis time, a material is selected so that separation at an interfacebetween the supporting base material and the separation layer, at aninterface between the separation layer and the insulating layer, or inthe separation layer occurs.

For example, it is preferable that a stacked layer of a layer includinga high-melting-point metal material, such as tungsten, and a layerincluding an oxide of the metal material be used as the separationlayer, and a stacked layer of a plurality of layers, such as a siliconnitride layer and a silicon oxynitride layer be used over the separationlayer. The use of the high-melting-point metal material is preferablebecause the degree of freedom of the process for forming the elementlayer can be increased.

The separation may be performed by application of mechanical power, byetching of the separation layer, by dripping of a liquid into part ofthe separation interface to penetrate the entire separation interface,or the like. Alternatively, separation may be performed by heating theseparation interface by utilizing a difference in of thermal expansioncoefficient.

The peeling layer is not necessarily provided in the case where peelingcan occur at an interface between the supporting base material and theinsulating layer. For example, glass may be used as the supporting basematerial, an organic resin such as polyimide may be used as theinsulating layer, a separation trigger may be formed by locally heatingpart of the organic resin by laser light or the like, and peeling may beperformed at an interface between the glass and the insulating layer.Alternatively, a metal layer may be provided between the supporting basematerial and the insulating layer formed of an organic resin, andseparation may be performed at the interface between the metal layer andthe insulating layer by heating the metal layer by feeding a current tothe metal layer. In that case, the insulating layer formed of an organicresin can be used as a base material.

Examples of such a base material having flexibility include polyesterresins such as polyethylene terephthalate (PET) and polyethylenenaphthalate (PEN), a polyacrylonitrile resin, a polyimide resin, apolymethyl methacrylate resin, a polycarbonate (PC) resin, apolyethersulfone (PES) resin, a polyamide resin, a cycloolefin resin, apolystyrene resin, a polyamide imide resin, and a polyvinyl chlorideresin. In particular, a material whose thermal expansion coefficient islow, for example, lower than or equal to 30×10⁻⁶/K is preferable, and apolyamide imide resin, a polyimide resin, or PET can be suitably used. Asubstrate in which a fibrous body is impregnated with a resin (alsoreferred to as prepreg) or a substrate whose thermal expansioncoefficient is reduced by mixing an inorganic filler with an organicresin can also be used.

In the case where a fibrous body is included in the above material, ahigh-strength fiber of an organic compound or an inorganic compound isused as the fibrous body. The high-strength fiber is specifically afiber with a high tensile modulus of elasticity or a fiber with a highYoung's modulus. Typical examples thereof include a polyvinyl alcoholbased fiber, a polyester based fiber, a polyamide based fiber, apolyethylene based fiber, an aramid based fiber, a polyparaphenylenebenzobisoxazole fiber, a glass fiber, and a carbon fiber. As the glassfiber, glass fiber using E glass, S glass, D glass, Q glass, or the likecan be used. These fibers may be used in a state of a woven fabric or anonwoven fabric, and a structure body in which this fibrous body isimpregnated with a resin and the resin is cured may be used as theflexible substrate. The structure body including the fibrous body andthe resin is preferably used as the flexible substrate, in which casethe reliability against bending or breaking due to local pressure can beincreased.

Note that for a display device of one embodiment of the presentinvention, an active matrix method in which an active element isincluded in a pixel or a passive matrix method in which an activeelement is not included in a pixel can be used.

In an active matrix method, as an active element (a non-linear element),not only a transistor but also various active elements (non-linearelements) can be used. For example, a metal insulator metal (MIM), athin film diode (TFD), or the like can also be used. Since such anelement has a small number of manufacturing steps, manufacturing costcan be reduced or yield can be improved. Alternatively, since the sizeof the element is small, the aperture ratio can be improved, so thatpower consumption can be reduced or higher luminance can be achieved.

As a method other than the active matrix method, the passive matrixmethod in which an active element (a non-linear element) is not used canalso be used. When an active element (a non-linear element) is not used,the number of manufacturing steps is small, so that manufacturing costcan be reduced or the yield can be improved. Alternatively, when anactive element (a non-linear element) is not used, the aperture ratiocan be improved, so that power consumption can be reduced or higherluminance can be achieved, for example.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Embodiment 3

In this embodiment, a structure of a foldable touch panel that can beused in the electronic device of one embodiment of the present inventionwill be described with reference to FIGS. 10A to 10C.

FIGS. 10A to 10C are cross-sectional views of a touch panel 500.

The touch panel 500 includes a display portion 501 and a touch sensor595. Furthermore, the touch panel 500 includes a substrate 510, asubstrate 570, and a substrate 590. Note that the substrate 510, thesubstrate 570, and the substrate 590 each have flexibility.

The display portion 501 includes the substrate 510, a plurality ofpixels over the substrate 510, and a plurality of wirings 511 throughwhich signals are supplied to the pixels. The plurality of wirings 511is led to a peripheral portion of the substrate 510, and part of theplurality of wirings 511 forms a terminal 519. The terminal 519 iselectrically connected to an FPC 509(1).

<Touch Sensor>

The substrate 590 includes the touch sensor 595 and a plurality ofwirings 598 electrically connected to the touch sensor 595. Theplurality of wirings 598 is led to a peripheral portion of the substrate590, and part of the plurality of wirings 598 forms a terminal. Theterminal is electrically connected to an FPC 509(2).

As the touch sensor 595, a capacitive touch sensor can be used. Examplesof the capacitive touch sensor are a surface capacitive touch sensor anda projected capacitive touch sensor.

Examples of the projected capacitive touch sensor are a self capacitivetouch sensor and a mutual capacitive touch sensor, which differ mainlyin the driving method. The use of a mutual capacitive touch sensor ispreferable because multiple points can be sensed simultaneously.

An example of using a projected capacitive touch sensor will bedescribed below.

Note that a variety of sensors that can sense the closeness or thecontact of a sensing target such as a finger, can be used.

The projected capacitive touch sensor 595 includes electrodes 591 andelectrodes 592. The electrodes 591 are electrically connected to any ofthe plurality of wirings 598, and the electrodes 592 are electricallyconnected to any of the other wirings 598.

A wiring 594 electrically connects two electrodes 591 between which theelectrode 592 is positioned. The intersecting area of the electrode 592and the wiring 594 is preferably as small as possible. Such a structureallows a reduction in the area of a region where the electrodes are notprovided, reducing unevenness in transmittance. As a result, unevennessin luminance of light from the touch sensor 595 can be reduced.

Note that the shapes of the electrodes 591 and the electrodes 592 can beany of a variety of shapes. For example, the plurality of electrodes 591may be provided so that a space between the electrodes 591 is reduced asmuch as possible, and a plurality of electrodes 592 may be provided withan insulating layer sandwiched between the electrodes 591 and theelectrodes 592 and may be spaced apart from each other to form a regionnot overlapping with the electrodes 591. In that case, between twoadjacent electrodes 592, it is preferable to provide a dummy electrodewhich is electrically insulated from these electrodes, whereby the areaof a region having a different transmittance can be reduced.

The touch sensor 595 includes the substrate 590, the electrodes 591 andthe electrodes 592 provided in a staggered arrangement on the substrate590, an insulating layer 593 covering the electrodes 591 and theelectrodes 592, and the wiring 594 that electrically connects theadjacent electrodes 591 to each other.

An adhesive layer 597 attaches the substrate 590 to the substrate 570 sothat the touch sensor 595 overlaps with the display portion 501.

The electrodes 591 and the electrodes 592 are formed using alight-transmitting conductive material. As the light-transmittingconductive material, a conductive oxide such as indium oxide, indium tinoxide, indium zinc oxide, zinc oxide, or zinc oxide to which gallium isadded, or graphene can be used.

The electrodes 591 and the electrodes 592 may be formed by depositing alight-transmitting conductive material on the substrate 590 by asputtering method and then removing an unnecessary portion by any ofvarious patterning techniques such as photolithography. Graphene may beformed in such a manner that a solution in which graphene oxide isdispersed is applied and reduced, in addition to a CVD method.

Examples of a material for the insulating layer 593 are a resin such asacrylic or epoxy resin, a resin having a siloxane bond, and an inorganicinsulating material such as silicon oxide, silicon oxynitride, oraluminum oxide.

Furthermore, openings reaching the electrodes 591 are formed in theinsulating layer 593, and the wiring 594 electrically connects theadjacent electrodes 591. A light-transmitting conductive material can befavorably used as the wiring 594 because the aperture ratio of the touchpanel can be increased. Moreover, a material with higher conductivitythan the conductivities of the electrodes 591 and 592 can be favorablyused because electric resistance can be reduced.

One electrode 592 extends in one direction, and a plurality ofelectrodes 592 is provided in the form of stripes.

The wiring 594 intersects with the electrode 592.

Adjacent electrodes 591 are provided with one electrode 592 providedtherebetween. The wiring 594 electrically connects the adjacentelectrodes 591.

Note that the plurality of electrodes 591 is not necessarily arranged inthe direction orthogonal to one electrode 592 and may be arranged tointersect with one electrode 592 at an angle of less than 90 degrees.

One wiring 598 is electrically connected to any of the electrodes 591and 592. Part of the wiring 598 serves as a terminal. For the wiring598, a metal material such as aluminum, gold, platinum, silver, nickel,titanium, tungsten, chromium, molybdenum, iron, cobalt, copper, orpalladium or an alloy material containing any of these metal materialscan be used.

Note that an insulating layer that covers the insulating layer 593 andthe wiring 594 may be provided to protect the touch sensor 595.

Furthermore, a connection layer 599 electrically connects the wiring 598to the FPC 509(2).

As the connection layer 599, any of anisotropic conductive films (ACF),anisotropic conductive pastes (ACP), and the like can be used.

The adhesive layer 597 has a light-transmitting property. For example, athermosetting resin or an ultraviolet curable resin can be used;specifically, a resin such as an acrylic resin, an urethane resin, anepoxy resin, or a resin having a siloxane bond can be used.

<Display Portion>

The display portion 501 includes a plurality of pixels arranged in amatrix. Each of the pixels includes a display element and a pixelcircuit for driving the display element.

In this embodiment, an example of using an organic electroluminescentelement that emits white light as a display element will be described;however, the display element is not limited to such element.

Other than organic electroluminescent elements, any of various displayelements such as display elements (electronic ink) that perform displayby an electrophoretic method, an electronic liquid powder method, or thelike; MEMS shutter display elements; and optical interference type MEMSdisplay elements can be used. A structure suitable for employed displayelements can be selected from among a variety of structures of pixelcircuits.

The substrate 510 is a stacked body in which a flexible substrate 510 b,a barrier film 510 a that prevents diffusion of unintentional impuritiesto light-emitting elements, and an adhesive layer 510 c that attachesthe barrier film 510 a to the substrate 510 b are stacked.

The substrate 570 is a stacked body in which a flexible substrate 570 b,a barrier film 570 a that prevents diffusion of unintentional impuritiesto the light-emitting elements, and an adhesive layer 570 c thatattaches the barrier film 570 a to the substrate 570 b are stacked.

A sealant 560 attaches the substrate 570 to the substrate 510. Thesealant 560 has a refractive index higher than that of air. In the caseof extracting light to the sealant 560 side, the sealant 560 serves asan optical adhesive layer. The pixel circuits and the light-emittingelements (e.g., a light-emitting element 550R) are provided between thesubstrate 510 and the substrate 570.

<<Structure of Pixel>>

A pixel includes a sub-pixel 502R, and the sub-pixel 502R includes alight-emitting module 580R.

The sub-pixel 502R includes the light-emitting element 550R and thepixel circuit that can supply electric power to the light-emittingelement 550R and includes a transistor 502 t. Furthermore, thelight-emitting module 580R includes the light-emitting element 550R andan optical element (e.g., a coloring layer 567R).

The light-emitting element 550R includes a lower electrode, an upperelectrode, and a layer containing a light-emitting organic compoundbetween the lower electrode and the upper electrode.

The light-emitting module 580R includes the coloring layer 567R on thelight extraction side. The coloring layer transmits light of aparticular wavelength and is, for example, a layer that selectivelytransmits light of red, green, or blue color. Note that in anothersub-pixel, a region that transmits light emitted from the light-emittingelement as it is may be provided as well.

In the case where the sealant 560 is provided on the light extractionside, the sealant 560 is in contact with the light-emitting element 550Rand the coloring layer 567R.

The coloring layer 567R is positioned in a region overlapping with thelight-emitting element 550R. Accordingly, part of light emitted from thelight-emitting element 550R passes through the coloring layer 567R andis emitted to the outside of the light-emitting module 580R as indicatedby an arrow in FIG. 10A.

<<Structure of Display Portion>>

The display portion 501 includes a light-blocking layer 567BM on thelight extraction side. The light-blocking layer 567BM is provided so asto surround the coloring layer (e.g., the coloring layer 567R).

The display portion 501 includes an anti-reflective layer 567 ppositioned in a region overlapping with pixels. As the anti-reflectivelayer 567 p, a circular polarizing plate can be used, for example.

The display portion 501 includes an insulating film 521. The insulatingfilm 521 covers the transistor 502 t. Note that the insulating film 521can be used as a layer for planarizing unevenness caused by the pixelcircuits. A stacked film including a layer that can prevent diffusion ofimpurities can be used as the insulating film 521. This can prevent thereliability of the transistor 502 t or the like from being lowered bydiffusion of unintentional impurities.

The display portion 501 includes the light-emitting elements (e.g., thelight-emitting element 550R) over the insulating film 521.

The display portion 501 includes, over the insulating film 521, apartition 528 that overlaps with an end portion of a lower electrode. Inaddition, a spacer that controls the distance between the substrate 510and the substrate 570 is provided on the partition 528.

<<Structure of Scan Line Driver Circuit>>

A scan line driver circuit 503 g(1) includes a transistor 503 t and acapacitor 503 c. Note that the driver circuit can be formed in the sameprocess and over the same substrate as those of the pixel circuits.

<<Other Structures>>

The display portion 501 includes the wirings 511 through which signalscan be supplied. The wirings 511 are provided with the terminal 519.Note that the FPC 509(1) through which a signal such as an image signalor a synchronization signal can be supplied is electrically connected tothe terminal 519.

Note that a printed wiring board (PWB) may be attached to the FPC509(1).

Modification Example 1 of Display Portion

Any of various kinds of transistors can be used in the display portion501.

A structure in the case of using bottom-gate transistors in the displayportion 501 is illustrated in FIGS. 10A and 10B.

For example, a semiconductor layer containing an oxide semiconductor,amorphous silicon, or the like can be used in the transistor 502 t andthe transistor 503 t illustrated in FIG. 10A.

For example, a semiconductor layer containing polycrystalline silicon orthe like can be used in the transistor 502 t and the transistor 503 tillustrated in FIG. 10B.

A structure in the case of using top-gate transistors in the displayportion 501 is illustrated in FIG. 10C.

For example, a semiconductor layer containing polycrystalline silicon, atransferred single crystal silicon film, or the like can be used in thetransistor 502 t and the transistor 503 t illustrated in FIG. 10C.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Embodiment 4

In this embodiment, a structure of a foldable touch panel that can beused in the electronic device of one embodiment of the present inventionwill be described with reference to FIGS. 11A to 11C.

FIGS. 11A to 11C are cross-sectional views of a touch panel 500B.

The touch panel 500B described in this embodiment is different from thetouch panel 500 described in Embodiment 3 in that the display portion501 displays received image data to the side where the transistors areprovided and that the touch sensor is provided on the substrate 510 sideof the display portion. Different structures will be described in detailbelow, and the above description is referred to for the other similarstructures.

<Display Portion>

The display portion 501 includes a plurality of pixels arranged in amatrix. Each of the pixels includes a display element and a pixelcircuit for driving the display element.

<<Structure of Pixel>>

A pixel includes the sub-pixel 502R, and the sub-pixel 502R includes alight-emitting module 580R.

The sub-pixel 502R includes the light-emitting element 550R and thepixel circuit that can supply electric power to the light-emittingelement 550R and includes the transistor 502 t.

The light-emitting module 580R includes the light-emitting element 550Rand an optical element (e.g., the coloring layer 567R).

The light-emitting element 550R includes a lower electrode, an upperelectrode, and a layer containing a light-emitting organic compoundbetween the lower electrode and the upper electrode.

The light-emitting module 580R includes the coloring layer 567R on thelight extraction side. The coloring layer transmits light of aparticular wavelength and is, for example, a layer that selectivelytransmits light of red, green, or blue color. Note that in anothersub-pixel, a region that transmits light emitted from the light-emittingelement as it is may be provided as well.

The coloring layer 567R is positioned in a region overlapping with thelight-emitting element 550R. The light-emitting element 550R illustratedin FIG. 11A emits light to the side where the transistor 502 t isprovided. Accordingly, part of light emitted from the light-emittingelement 550R passes through the coloring layer 567R and is emitted tothe outside of the light-emitting module 580R as indicated by an arrowin FIG. 11A.

<<Structure of Display Portion>>

The display portion 501 includes a light-blocking layer 567BM on thelight extraction side. The light-blocking layer 567BM is provided so asto surround the coloring layer (e.g., the coloring layer 567R).

The display portion 501 includes an insulating film 521. The insulatingfilm 521 covers the transistor 502 t. Note that the insulating film 521can be used as a layer for planarizing unevenness caused by the pixelcircuits. A stacked film including a layer that can prevent diffusion ofimpurities can be used as the insulating film 521. This can prevent thereliability of the transistor 502 t or the like from being lowered bydiffusion of unintentional impurities from the coloring layer 567R.

<Touch Sensor>

The touch sensor 595 is provided on the substrate 510 side of thedisplay portion 501 (see FIG. 11A).

The adhesive layer 597 is provided between the substrate 510 and thesubstrate 590 and attaches the touch sensor 595 to the display portion501.

Modification Example 1 of Display Portion

Any of various kinds of transistors can be used in the display portion501.

A structure in the case of using bottom-gate transistors in the displayportion 501 is illustrated in FIGS. 11A and 11B.

For example, a semiconductor layer containing an oxide semiconductor,amorphous silicon, or the like can be used in the transistor 502 t andthe transistor 503 t illustrated in FIG. 11A.

For example, a semiconductor layer containing polycrystalline silicon orthe like can be used in the transistor 502 t and the transistor 503 tillustrated in FIG. 1B.

A structure in the case of using top-gate transistors in the displayportion 501 is illustrated in FIG. 11C.

For example, a semiconductor layer containing polycrystalline silicon, atransferred single crystal silicon film, or the like can be used in thetransistor 502 t and the transistor 503 t illustrated in FIG. 11C.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Embodiment 5

An oxide semiconductor suitable for a semiconductor layer of asemiconductor device that can be used for a display panel of oneembodiment of the present invention is described in this embodiment.

An oxide semiconductor has a wide energy gap of 3.0 eV or more. Atransistor including an oxide semiconductor film obtained by processingof the oxide semiconductor in an appropriate condition and a sufficientreduction in carrier density of the oxide semiconductor can have muchlower leakage current between a source and a drain in an off state(off-state current) than a conventional transistor including silicon.

An applicable oxide semiconductor preferably contains at least indium(In) or zinc (Zn). In particular, In and Zn are preferably contained. Inaddition, as a stabilizer for reducing variation in electricalcharacteristics of the transistor using the oxide semiconductor, one ormore selected from gallium (Ga), tin (Sn), hafnium (Hf), zirconium (Zr),titanium (Ti), scandium (Sc), yttrium (Y), and an lanthanoid (e.g.,cerium (Ce), neodymium (Nd), or gadolinium (Gd)) is preferablycontained.

As the oxide semiconductor, for example, any of the following can beused: indium oxide, tin oxide, zinc oxide, an In—Zn-based oxide, aSn—Zn-based oxide, an Al—Zn-based oxide, a Zn—Mg-based oxide, aSn—Mg-based oxide, an In—Mg-based oxide, an In—Ga-based oxide, anIn—Ga—Zn-based oxide (also referred to as IGZO), an In—Al—Zn-basedoxide, an In—Sn—Zn-based oxide, a Sn—Ga—Zn-based oxide, anAl—Ga—Zn-based oxide, a Sn—Al—Zn-based oxide, an In—Hf—Zn-based oxide,an In—Zr—Zn-based oxide, an In—Ti—Zn-based oxide, an In—Sc—Zn-basedoxide, an In—Y—Zn-based oxide, an In—La—Zn-based oxide, anIn—Ce—Zn-based oxide, an In—Pr—Zn-based oxide, an In—Nd—Zn-based oxide,an In—Sm—Zn-based oxide, an In—Eu—Zn-based oxide, an In—Gd—Zn-basedoxide, an In—Tb—Zn-based oxide, an In—Dy—Zn-based oxide, anIn—Ho—Zn-based oxide, an In—Er—Zn-based oxide, an In—Tm—Zn-based oxide,an In—Yb—Zn-based oxide, an In—Lu—Zn-based oxide, an In—Sn—Ga—Zn-basedoxide, an In—Hf—Ga—Zn-based oxide, an In—Al—Ga—Zn-based oxide, anIn—Sn—Al—Zn-based oxide, an In—Sn—Hf—Zn-based oxide, or anIn—Hf—Al—Zn-based oxide.

Here, an “In—Ga—Zn-based oxide” means an oxide containing In, Ga, and Znas its main components and there is no particular limitation on theratio of In:Ga:Zn. The In—Ga—Zn-based oxide may contain a metal elementother than the In, Ga, and Zn.

Alternatively, a material represented by InMO₃(ZnO)_(m) (m>0 issatisfied, and m is not an integer) may be used as an oxidesemiconductor. Note that M represents one or more metal elementsselected from Ga, Fe, Mn, and Co, or the above-described element as astabilizer. Alternatively, as the oxide semiconductor, a materialexpressed by a chemical formula, In₂SnO₅(ZnO)_(n) (n>0, n is an integer)may be used.

For example, In—Ga—Zn-based oxide with an atomic ratio ofIn:Ga:Zn=1:1:1, 1:3:2, 1:3:4, 1:3:6, 3:1:2, or 2:1:3, or an oxide whosecomposition is in the neighborhood of the above compositions may beused.

Note that if the oxide semiconductor film contains a large amount ofhydrogen, the hydrogen and the oxide semiconductor are bonded to eachother, so that part of the hydrogen serves as a donor and causesgeneration of an electron that is a carrier. As a result, the thresholdvoltage of the transistor shifts in the negative direction. Therefore,it is preferable that, after formation of the oxide semiconductor film,dehydration treatment (dehydrogenation treatment) be performed to removehydrogen or moisture from the oxide semiconductor film so that the oxidesemiconductor film is highly purified to contain impurities as little aspossible.

Note that oxygen in the oxide semiconductor film is also reduced by thedehydration treatment (dehydrogenation treatment) in some cases.Therefore, it is preferable that oxygen be added to the oxidesemiconductor film to fill oxygen vacancies increased by the dehydrationtreatment (dehydrogenation treatment). In this specification and thelike, supplying oxygen to an oxide semiconductor film may be expressedas oxygen adding treatment, or treatment for making the oxygen contentof an oxide semiconductor film be in excess of that of thestoichiometric composition may be expressed as treatment for making anoxygen-excess state.

In this manner, hydrogen or moisture is removed from the oxidesemiconductor film by the dehydration treatment (dehydrogenationtreatment) and oxygen vacancies therein are filled by the oxygen addingtreatment, so that the oxide semiconductor film can be an i-type(intrinsic) oxide semiconductor film or an oxide semiconductor filmextremely close to an i-type oxide semiconductor (a substantially i-typeoxide semiconductor). Note that “substantially intrinsic” means that theoxide semiconductor film includes extremely few (close to zero) carriersderived from a donor, and the carrier concentration thereof is lowerthan or equal to 1×10¹⁷/cm³, lower than or equal to 1×10¹⁶/cm³, lowerthan or equal to 1×10¹⁵/cm³, lower than or equal to 1×10¹⁴/cm, or lowerthan or equal to 1×10³/cm³.

In this manner, the transistor including an i-type or substantiallyi-type oxide semiconductor film can have extremely favorable off-statecurrent characteristics. For example, the drain current at the time whenthe transistor including an oxide semiconductor film is in an off-stateat room temperature (25° C.) can be less than or equal to 1×10⁻¹⁸ A,preferably less than or equal to 1×10⁻²¹ A, further preferably less thanor equal to 1×10⁻²⁴ A; or at 85° C., less than or equal to 1×10⁻¹⁵ A,preferably less than or equal to 1×10⁻¹⁸ A, further preferably less thanor equal to 1×10⁻²¹ A. An off state of a transistor refers to a statewhere gate voltage is lower than the threshold voltage in an n-channeltransistor. Specifically, the transistor is in an off state when thegate voltage is lower than the threshold voltage by 1 V or more, 2 V ormore, or 3 V or more.

A structure of the oxide semiconductor film is described below.

In this specification, the term “parallel” indicates that the angleformed between two straight lines is greater than or equal to −10° andless than or equal to 100, and accordingly also includes the case wherethe angle is greater than or equal to −5° and less than or equal to 50.The term “substantially parallel” indicates that the angle formedbetween two straight lines is greater than or equal to −30° and lessthan or equal to 30°. The term “perpendicular” indicates that the angleformed between two straight lines is greater than or equal to 80° andless than or equal to 1000, and accordingly includes the case where theangle is greater than or equal to 85° and less than or equal to 95°. Theterm “substantially perpendicular” indicates that the angle formedbetween two straight lines is greater than or equal to 60° and less thanor equal to 120°.

In this specification, trigonal and rhombohedral crystal systems areincluded in a hexagonal crystal system.

An oxide semiconductor is classified into a single crystal oxidesemiconductor and a non-single-crystal oxide semiconductor. Examples ofa non-single-crystal oxide semiconductor include a c-axis alignedcrystalline oxide semiconductor (CAAC-OS), a polycrystalline oxidesemiconductor, a microcrystalline oxide semiconductor, and an amorphousoxide semiconductor.

From another perspective, an oxide semiconductor is classified into anamorphous oxide semiconductor and a crystalline oxide semiconductor.Examples of a crystalline oxide semiconductor include a single crystaloxide semiconductor, a CAAC-OS, a polycrystalline oxide semiconductor,and a microcrystalline oxide semiconductor.

First, a CAAC-OS is described. Note that a CAAC-OS can be referred to asan oxide semiconductor including c-axis aligned nanocrystals (CANC).

A CAAC-OS is one of oxide semiconductors having a plurality of c-axisaligned crystal parts (also referred to as pellets).

In a combined analysis image (also referred to as a high-resolution TEMimage) of a bright-field image and a diffraction pattern of a CAAC-OS,which is obtained using a transmission electron microscope (TEM), aplurality of pellets can be observed. However, in the high-resolutionTEM image, a boundary between pellets, that is, a grain boundary is notclearly observed. Thus, in the CAAC-OS, a reduction in electron mobilitydue to the grain boundary is less likely to occur.

A CAAC-OS observed with TEM is described below. FIG. 12A shows ahigh-resolution TEM image of a cross section of the CAAC-OS which isobserved from a direction substantially parallel to the sample surface.The high-resolution TEM image is obtained with a spherical aberrationcorrector function. The high-resolution TEM image obtained with aspherical aberration corrector function is particularly referred to as aCs-corrected high-resolution TEM image. The Cs-corrected high-resolutionTEM image can be obtained with, for example, an atomic resolutionanalytical electron microscope JEM-ARM200F manufactured by JEOL Ltd.

FIG. 12B is an enlarged Cs-corrected high-resolution TEM image of aregion (1) in FIG. 12A. FIG. 12B shows that metal atoms are arranged ina layered manner in a pellet. Each metal atom layer has a configurationreflecting unevenness of a surface over which the CAAC-OS is formed(hereinafter, the surface is referred to as a formation surface) or atop surface of the CAAC-OS, and is arranged parallel to the formationsurface or the top surface of the CAAC-OS.

As shown in FIG. 12B, the CAAC-OS has a characteristic atomicarrangement. The characteristic atomic arrangement is denoted by anauxiliary line in FIG. 12C. FIGS. 12B and 12C prove that the size of apellet is approximately 1 nm to 3 nm, and the size of a space caused bytilt of the pellets is approximately 0.8 nm. Therefore, the pellet canalso be referred to as a nanocrystal (nc).

Here, according to the Cs-corrected high-resolution TEM images, theschematic arrangement of pellets 5100 of a CAAC-OS over a substrate 5120is illustrated by such a structure in which bricks or blocks are stacked(see FIG. 12D). The part in which the pellets are tilted as observed inFIG. 12C corresponds to a region 5161 shown in FIG. 12D.

FIG. 13A shows a Cs-corrected high-resolution TEM image of a plane ofthe CAAC-OS observed from a direction substantially perpendicular to thesample surface. FIGS. 13B, 13C, and 13D are enlarged Cs-correctedhigh-resolution TEM images of regions (1), (2), and (3) in FIG. 13A,respectively. FIGS. 13B, 13C, and 13D indicate that metal atoms arearranged in a triangular, quadrangular, or hexagonal configuration in apellet. However, there is no regularity of arrangement of metal atomsbetween different pellets.

Next, a CAAC-OS analyzed by X-ray diffraction (XRD) is described. Forexample, when the structure of a CAAC-OS including an InGaZnO₄ crystalis analyzed by an out-of-plane method, a peak appears at a diffractionangle (2θ) of around 31° as shown in FIG. 14A. This peak is derived fromthe (009) plane of the InGaZnO₄ crystal, which indicates that crystalsin the CAAC-OS have c-axis alignment, and that the c-axes are aligned ina direction substantially perpendicular to the formation surface or thetop surface of the CAAC-OS.

Note that in structural analysis of the CAAC-OS by an out-of-planemethod, another peak may appear when 2θ is around 36°, in addition tothe peak at 2θ of around 31°. The peak at 2θ of around 36° indicatesthat a crystal having no c-axis alignment is included in part of theCAAC-OS. It is preferable that in the CAAC-OS analyzed by anout-of-plane method, a peak appear when 2θ is around 31° and that a peaknot appear when 2θ is around 36°.

On the other hand, in structural analysis of the CAAC-OS by an in-planemethod in which an X-ray is incident on a sample in a directionsubstantially perpendicular to the c-axis, a peak appears when 2θ isaround 56°. This peak is attributed to the (110) plane of the InGaZnO₄crystal. In the case of the CAAC-OS, when analysis (ϕ scan) is performedwith 29 fixed at around 56° and with the sample rotated using a normalvector of the sample surface as an axis (q axis), as shown in FIG. 14B,a peak is not clearly observed. In contrast, in the case of a singlecrystal oxide semiconductor of InGaZnO₄, when ϕ scan is performed with 2fixed at around 56°, as shown in FIG. 14C, six peaks which are derivedfrom crystal planes equivalent to the (110) plane are observed.Accordingly, the structural analysis using XRD shows that the directionsof a-axes and b-axes are different in the CAAC-OS.

Next, a CAAC-OS analyzed by electron diffraction is described. Forexample, when an electron beam with a probe diameter of 300 nm isincident on a CAAC-OS including an InGaZnO₄ crystal in a directionparallel to the sample surface, a diffraction pattern (also referred toas a selected-area transmission electron diffraction pattern) shown inFIG. 15A might be obtained. In this diffraction pattern, spots derivedfrom the (009) plane of an InGaZnO₄ crystal are included. Thus, theelectron diffraction also indicates that pellets included in the CAAC-OShave c-axis alignment and that the c-axes are aligned in a directionsubstantially perpendicular to the formation surface or the top surfaceof the CAAC-OS. Meanwhile, FIG. 15B shows a diffraction pattern obtainedin such a manner that an electron beam with a probe diameter of 300 nmis incident on the same sample in a direction perpendicular to thesample surface. As shown in FIG. 15B, a ring-like diffraction pattern isobserved. Thus, the electron diffraction also indicates that the a-axesand b-axes of the pellets included in the CAAC-OS do not have regularalignment. The first ring in FIG. 15B is considered to be derived fromthe (010) plane, the (100) plane, and the like of the InGaZnO₄ crystal.The second ring in FIG. 15B is considered to be derived from the (110)plane and the like.

Moreover, the CAAC-OS is an oxide semiconductor having a low density ofdefect states. Defects in the oxide semiconductor are, for example, adefect due to impurity and oxygen vacancies. Therefore, the CAAC-OS canbe regarded as an oxide semiconductor with a low impurity concentration,or an oxide semiconductor having a small number of oxygen vacancies.

The impurity contained in the oxide semiconductor might serve as acarrier trap or serve as a carrier generation source. Furthermore,oxygen vacancies in the oxide semiconductor serve as carrier traps orserve as carrier generation sources when hydrogen is captured therein.

Note that the impurity means an element other than the main componentsof the oxide semiconductor, such as hydrogen, carbon, silicon, or atransition metal element. For example, an element (specifically, siliconor the like) having higher strength of bonding to oxygen than a metalelement included in an oxide semiconductor extracts oxygen from theoxide semiconductor, which results in disorder of the atomic arrangementand reduced crystallinity of the oxide semiconductor. A heavy metal suchas iron or nickel, argon, carbon dioxide, or the like has a large atomicradius (or molecular radius), and thus disturbs the atomic arrangementof the oxide semiconductor and decreases crystallinity.

An oxide semiconductor having a low density of defect states (a smallnumber of oxygen vacancies) can have a low carrier density. Such anoxide semiconductor is referred to as a highly purified intrinsic orsubstantially highly purified intrinsic oxide semiconductor. A CAAC-OShas a low impurity concentration and a low density of defect states.That is, a CAAC-OS is likely to be a highly purified intrinsic orsubstantially highly purified intrinsic oxide semiconductor. Thus, atransistor including a CAAC-OS rarely has negative threshold voltage (israrely normally on). The highly purified intrinsic or substantiallyhighly purified intrinsic oxide semiconductor has few carrier traps. Anelectric charge trapped by the carrier traps in the oxide semiconductortakes a long time to be released. The trapped electric charge may behavelike a fixed electric charge. Thus, the transistor which includes theoxide semiconductor having a high impurity concentration and a highdensity of defect states might have unstable electrical characteristics.However, a transistor including a CAAC-OS has small variation inelectrical characteristics and high reliability.

Since the CAAC-OS has a low density of defect states, carriers generatedby light irradiation or the like are less likely to be trapped in defectstates. Therefore, in a transistor using the CAAC-OS, change inelectrical characteristics due to irradiation with visible light orultraviolet light is small.

Next, a microcrystalline oxide semiconductor is described.

A microcrystalline oxide semiconductor has a region in which a crystalpart is observed and a region in which a crystal part is not clearlyobserved in a high-resolution TEM image. In most cases, the size of acrystal part included in the microcrystalline oxide semiconductor isgreater than or equal to 1 nm and less than or equal to 100 nm, orgreater than or equal to 1 nm and less than or equal to 10 nm. An oxidesemiconductor including a nanocrystal (nc) that is a microcrystal with asize greater than or equal to 1 nm and less than or equal to 10 nm, or asize greater than or equal to 1 nm and less than or equal to 3 nm isspecifically referred to as a nanocrystalline oxide semiconductor(nc-OS). In a high-resolution TEM image of the nc-OS, for example, agrain boundary is not clearly observed in some cases. Note that there isa possibility that the origin of the nanocrystal is the same as that ofa pellet in a CAAC-OS. Therefore, a crystal part of the nc-OS may bereferred to as a pellet in the following description.

In the nc-OS, a microscopic region (for example, a region with a sizegreater than or equal to 1 nm and less than or equal to 10 nm, inparticular, a region with a size greater than or equal to 1 nm and lessthan or equal to 3 nm) has a periodic atomic arrangement. There is noregularity of crystal orientation between different pellets in thenc-OS. Thus, the orientation of the whole film is not ordered.Accordingly, the nc-OS cannot be distinguished from an amorphous oxidesemiconductor, depending on an analysis method. For example, when thenc-OS is subjected to structural analysis by an out-of-plane method withan XRD apparatus using an X-ray having a diameter larger than the sizeof a pellet, a peak which shows a crystal plane does not appear.Furthermore, a diffraction pattern like a halo pattern is observed whenthe nc-OS is subjected to electron diffraction using an electron beamwith a probe diameter (e.g., 50 nm or larger) that is larger than thesize of a pellet (the electron diffraction is also referred to asselected-area electron diffraction). Meanwhile, spots appear in ananobeam electron diffraction pattern of the nc-OS when an electron beamhaving a probe diameter close to or smaller than the size of a pellet isapplied. Moreover, in a nanobeam electron diffraction pattern of thenc-OS, regions with high luminance in a circular (ring) pattern areshown in some cases. Also in a nanobeam electron diffraction pattern ofthe nc-OS, a plurality of spots is shown in a ring-like region in somecases.

Since there is no regularity of crystal orientation between the pellets(nanocrystals) as mentioned above, the nc-OS can also be referred to asan oxide semiconductor including random aligned nanocrystals (RANC) oran oxide semiconductor including non-aligned nanocrystals (NANC).

The nc-OS is an oxide semiconductor that has high regularity as comparedwith an amorphous oxide semiconductor. Therefore, the nc-OS is likely tohave a lower density of defect states than an amorphous oxidesemiconductor. Note that there is no regularity of crystal orientationbetween different pellets in the nc-OS. Therefore, the nc-OS has ahigher density of defect states than the CAAC-OS.

Next, an amorphous oxide semiconductor is described.

The amorphous oxide semiconductor is an oxide semiconductor havingdisordered atomic arrangement and no crystal part and exemplified by anoxide semiconductor which exists in an amorphous state as quartz.

In a high-resolution TEM image of the amorphous oxide semiconductor,crystal parts cannot be found.

When the amorphous oxide semiconductor is subjected to structuralanalysis by an out-of-plane method with an XRD apparatus, a peak whichshows a crystal plane does not appear. A halo pattern is observed whenthe amorphous oxide semiconductor is subjected to electron diffraction.Furthermore, a spot is not observed and only a halo pattern appears whenthe amorphous oxide semiconductor is subjected to nanobeam electrondiffraction.

There are various understandings of an amorphous structure. For example,a structure whose atomic arrangement does not have ordering at all iscalled a completely amorphous structure. Meanwhile, a structure whichhas ordering until the nearest neighbor atomic distance or thesecond-nearest neighbor atomic distance but does not have long-rangeordering is also called an amorphous structure. Therefore, the strictestdefinition does not permit an oxide semiconductor to be called anamorphous oxide semiconductor as long as even a negligible degree ofordering is present in an atomic arrangement. At least an oxidesemiconductor having long-term ordering cannot be called an amorphousoxide semiconductor. Accordingly, because of the presence of crystalpart, for example, a CAAC-OS and an nc-OS cannot be called an amorphousoxide semiconductor or a completely amorphous oxide semiconductor.

Note that an oxide semiconductor may have a structure intermediatebetween the nc-OS and the amorphous oxide semiconductor. The oxidesemiconductor having such a structure is specifically referred to as anamorphous-like oxide semiconductor (a-like OS).

In a high-resolution TEM image of the a-like OS, a void may be observed.Furthermore, in the high-resolution TEM image, there are a region wherea crystal part is clearly observed and a region where a crystal part isnot observed.

The a-like OS has an unstable structure because it includes a void. Toverify that an a-like OS has an unstable structure as compared with aCAAC-OS and an nc-OS, a change in structure caused by electronirradiation is described below.

An a-like OS (referred to as Sample A), an nc-OS (referred to as SampleB), and a CAAC-OS (referred to as Sample C) are prepared as samplessubjected to electron irradiation. Each of the samples is an In—Ga—Znoxide.

First, a high-resolution cross-sectional TEM image of each sample isobtained. The high-resolution cross-sectional TEM images show that allthe samples have crystal parts.

Note that a crystal part is determined as follows. It is known that aunit cell of an InGaZnO₄ crystal has a structure in which nine layersincluding three In—O layers and six Ga—Zn—O layers are stacked in thec-axis direction. The distance between the adjacent layers is equivalentto the lattice spacing on the (009) plane (also referred to as d value).The value is calculated to be 0.29 nm from crystal structural analysis.Accordingly, a portion where the lattice spacing between lattice fringesis greater than or equal to 0.28 nm and less than or equal to 0.30 nm isregarded as a crystal part of InGaZnO₄. Each of lattice fringescorresponds to the a-b plane of the InGaZnO₄ crystal.

FIG. 16 shows change in the average size of crystal parts (at 22 pointsto 45 points) in each sample. Note that the crystal part sizecorresponds to the length of a lattice fringe. FIG. 16 indicates thatthe crystal part size in the a-like OS increases with an increase in thecumulative electron dose. Specifically, as shown by (1) in FIG. 16, acrystal part of approximately 1.2 nm (also referred to as an initialnucleus) at the start of TEM observation grows to a size ofapproximately 2.6 nm at a cumulative electron dose of 4.2×10⁸ e⁻/nm². Incontrast, the crystal part size in the nc-OS and the CAAC-OS showslittle change from the start of electron irradiation to a cumulativeelectron dose of 4.2×10⁸e⁻/nm². Specifically, as shown by (2) and (3) inFIG. 16, the average crystal sizes in an nc-OS and a CAAC-OS areapproximately 1.4 nm and approximately 2.1 nm, respectively, regardlessof the cumulative electron dose.

In this manner, growth of the crystal part in the a-like OS is inducedby electron irradiation. In contrast, in the nc-OS and the CAAC-OS,growth of the crystal part is hardly induced by electron irradiation.Therefore, the a-like OS has an unstable structure as compared with thenc-OS and the CAAC-OS.

The a-like OS has a lower density than the nc-OS and the CAAC-OS becauseit includes a void. Specifically, the density of the a-like OS is higherthan or equal to 78.6% and lower than 92.3% of the density of the singlecrystal oxide semiconductor having the same composition. The density ofeach of the nc-OS and the CAAC-OS is higher than or equal to 92.3% andlower than 100% of the density of the single crystal oxide semiconductorhaving the same composition. Note that it is difficult to deposit anoxide semiconductor having a density of lower than 78% of the density ofthe single crystal oxide semiconductor.

For example, in the case of an oxide semiconductor having an atomicratio of In:Ga:Zn=1:1:1, the density of single crystal InGaZnO₄ with arhombohedral crystal structure is 6.357 g/cm³. Accordingly, in the caseof the oxide semiconductor having an atomic ratio of In:Ga:Zn=1:1:1, thedensity of the a-like OS is higher than or equal to 5.0 g/cm³ and lowerthan 5.9 g/cm³. For example, in the case of the oxide semiconductorhaving an atomic ratio of In:Ga:Zn=1:1:1, the density of each of thenc-OS and the CAAC-OS is higher than or equal to 5.9 g/cm³ and lowerthan 6.3 g/cm³.

Note that there is a possibility that an oxide semiconductor having acertain composition cannot exist in a single crystal structure. In thatcase, single crystal oxide semiconductors with different compositionsare combined at an adequate ratio, which makes it possible to calculatedensity equivalent to that of a single crystal oxide semiconductor withthe desired composition. The density of a single crystal oxidesemiconductor having the desired composition can be calculated using aweighted average according to the combination ratio of the singlecrystal oxide semiconductors with different compositions. Note that itis preferable to use as few kinds of single crystal oxide semiconductorsas possible to calculate the density.

As described above, oxide semiconductors have various structures andvarious properties. Note that an oxide semiconductor may be a stackedlayer including two or more films of an amorphous oxide semiconductor,an a-like OS, a microcrystalline oxide semiconductor, and a CAAC-OS, forexample.

The CAAC-OS film is formed, for example, by the following method.

For example, the CAAC-OS film is formed by a sputtering method with apolycrystalline oxide semiconductor sputtering target.

By increasing the substrate temperature during the deposition, migrationof sputtered particles is likely to occur after the sputtered particlesreach a substrate surface. Specifically, the substrate temperatureduring the deposition is higher than or equal to 100° C. and lower thanor equal to 740° C., preferably higher than or equal to 200° C. andlower than or equal to 500° C. By increasing the substrate temperatureduring the deposition, when the flat-plate-like or pellet-like sputteredparticles reach the substrate, migration occurs on the substratesurface, so that a flat plane of the sputtered particles is attached tothe substrate. At this time, the sputtered particle is chargedpositively, whereby sputtered particles are attached to the substratewhile repelling each other; thus, the sputtered particles do not overlapwith each other randomly, and a CAAC-OS film with a uniform thicknesscan be deposited.

By reducing the amount of impurities entering the CAAC-OS film duringthe deposition, the crystal state can be prevented from being broken bythe impurities. For example, the concentration of impurities (e.g.,hydrogen, water, carbon dioxide, or nitrogen) that exist in thedeposition chamber may be reduced. Furthermore, the concentration ofimpurities in a deposition gas may be reduced. Specifically, adeposition gas whose dew point is −80° C. or lower, preferably −100° C.or lower is used.

Furthermore, it is preferable that the proportion of oxygen in thedeposition gas be increased and the power be optimized in order toreduce plasma damage at the deposition. The proportion of oxygen in thedeposition gas is higher than or equal to 30 vol %, preferably 100 vol%.

Alternatively, the CAAC-OS film is formed by the following method.

First, a first oxide semiconductor film is formed to a thickness ofgreater than or equal to 1 nm and less than 10 nm. The first oxidesemiconductor film is formed by a sputtering method. Specifically, thesubstrate temperature is set to higher than or equal to 100° C. andlower than or equal to 500° C., preferably higher than or equal to 150°C. and lower than or equal to 450° C., and the proportion of oxygen in adeposition gas is set to higher than or equal to 30 vol %, preferably100 vol %.

Next, heat treatment is performed so that the first oxide semiconductorfilm becomes a first CAAC-OS film with high crystallinity. Thetemperature of the heat treatment is higher than or equal to 350° C. andlower than or equal to 740° C., preferably higher than or equal to 450°C. and lower than or equal to 650° C. The heat treatment time is longerthan or equal to 1 minute and shorter than or equal to 24 hours,preferably longer than or equal to 6 minutes and shorter than or equalto 4 hours. The heat treatment may be performed in an inert atmosphereor an oxidation atmosphere. It is preferable to perform heat treatmentin an inert atmosphere and then perform heat treatment in an oxidationatmosphere. The heat treatment in an inert atmosphere can reduce theconcentration of impurities in the first oxide semiconductor film for ashort time. At the same time, the heat treatment in an inert atmospheremay generate oxygen vacancies in the first oxide semiconductor film. Insuch a case, the heat treatment in an oxidation atmosphere can reducethe oxygen vacancies. Note that the heat treatment may be performedunder a reduced pressure, such as 1000 Pa or lower, 100 Pa or lower, 10Pa or lower, or 1 Pa or lower. The heat treatment under the reducedpressure can reduce the concentration of impurities in the first oxidesemiconductor film for a shorter time.

The first oxide semiconductor film with a thickness greater than orequal to 1 nm and less than 10 nm can be easily crystallized by heattreatment as compared to the case where the first oxide semiconductorfilm has a thickness greater than or equal to 10 nm.

Next, a second oxide semiconductor film having the same composition asthe first oxide semiconductor film is formed to a thickness of greaterthan or equal to 10 nm and less than or equal to 50 nm. The second oxidesemiconductor film is formed by a sputtering method. Specifically, thesubstrate temperature is set to higher than or equal to 100° C. andlower than or equal to 500° C., preferably higher than or equal to 150°C. and lower than or equal to 450° C., and the proportion of oxygen in adeposition gas is set to higher than or equal to 30 vol %, preferably100 vol %.

Next, heat treatment is performed so that solid phase growth of thesecond oxide semiconductor film is performed using the first CAAC-OSfilm, thereby forming a second CAAC-OS film with high crystallinity. Thetemperature of the heat treatment is higher than or equal to 350° C. andlower than or equal to 740° C., preferably higher than or equal to 450°C. and lower than or equal to 650° C. The heat treatment time is longerthan or equal to 1 minute and shorter than or equal to 24 hours,preferably longer than or equal to 6 minutes and shorter than or equalto 4 hours. The heat treatment may be performed in an inert atmosphereor an oxidation atmosphere. It is preferable to perform heat treatmentin an inert atmosphere and then perform heat treatment in an oxidationatmosphere. The heat treatment in an inert atmosphere can reduce theconcentration of impurities in the second oxide semiconductor film for ashort time. At the same time, the heat treatment in an inert atmospheremay generate oxygen vacancies in the second oxide semiconductor film. Insuch a case, the heat treatment in an oxidation atmosphere can reducethe oxygen vacancies. Note that the heat treatment may be performedunder a reduced pressure, such as 1000 Pa or lower, 100 Pa or lower, 10Pa or lower, or 1 Pa or lower. The heat treatment under the reducedpressure can reduce the concentration of impurities in the second oxidesemiconductor film for a shorter time.

In the above-described manner, a CAAC-OS film with a total thickness ofgreater than or equal to 10 nm can be formed.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

EXPLANATION OF REFERENCE

101: housing, 102: substrate, 103: FPC, 103 a: FPC, 104: IC, 105: touchsensor, 106: FPC, 110: display panel, 111: display region, 112: displayregion, 113: display region, 114: display region, 115: display region,121: icon, 122: text data, 123: icon, 124: text data, 125: slide bar,126: finger, 131: side, 132: side, 133: side, 138: notch portion, 141:driver circuit, 142: driver circuit, 143: driver circuit, 145: wiring,146: wiring, 300: touch panel, 301: display portion, 302: pixel, 302B:sub-pixel, 302G: sub-pixel, 302R: sub-pixel, 302 t: transistor, 303 c:capacitor, 303 g(1): scan line driver circuit, 303 g(2): imaging pixeldriver circuit, 303 s(1): image signal line driver circuit, 303 s(2):imaging signal line driver circuit, 303 t: transistor, 308: imagingpixel, 308 p: photoelectric conversion element, 308 t: transistor, 309:FPC, 310: substrate, 310 a: barrier film, 310 b: substrate, 310 c:adhesive layer, 311: wiring, 319: terminal, 321: insulating film, 328:partition, 329: spacer, 350R: light-emitting element, 351R: lowerelectrode, 352: upper electrode, 353: layer, 353 a: light-emitting unit,353 b: light-emitting unit, 354: intermediate layer, 360: sealant,367BM: light-blocking layer, 367 p: anti-reflective layer, 367R:coloring layer, 370: counter substrate, 370 a: barrier film, 370 b:substrate, 370 c: adhesive layer, 380B: light-emitting module, 380G:light-emitting module, 380R: light-emitting module, 500: touch panel,500B: touch panel, 501: display portion, 502R: sub-pixel, 502 t:transistor, 503 c: capacitor, 503 g(1): scan line driver circuit, 503 t:transistor, 509: FPC, 510: substrate, 510 a: barrier film, 510 b:substrate, 510 c: adhesive layer, 511: wiring, 519: terminal, 521:insulating film, 528: partition, 550R: light-emitting element, 560:sealant, 567BM: light-blocking layer, 567 p: anti-reflective layer,567R: coloring layer, 570: substrate, 570 a: barrier film, 570 b:substrate, 570 c: adhesive layer, 580R: light-emitting module, 590:substrate, 591: electrode, 592: electrode, 593: insulating layer, 594:wiring, 595: touch sensor, 597: adhesive layer, 598: wiring, 599:connection layer, 5100: pellet, 5120: substrate, and 5161: region.

This application is based on Japanese Patent Application serial no.2013-236969 filed with Japan Patent Office on Nov. 15, 2013, andJapanese Patent Application serial no. 2013-236966 filed with JapanPatent Office on Nov. 15, 2013, the entire contents of which are herebyincorporated by reference.

What is claimed is:
 1. An electronic device comprising: a housing; adisplay panel; and a flexible printed circuit, wherein the housingincludes a flat surface, and first, second, third, and fourth sidesurfaces that extend from the flat surface, wherein the first sidesurface is opposite to the fourth side surface, wherein the second sidesurface is opposite to the third side surface, wherein the first sidesurface and the fourth side surface are longer than the second sidesurface and the third side surface, wherein each of the first sidesurface and the fourth side surface includes a curved surface, whereinthe display panel includes a flexible substrate, wherein the flexiblesubstrate includes a first region and a second region, wherein the firstregion overlaps with the flat surface, the first side surface, and thefourth side surface, wherein the second region overlaps with the secondside surface, wherein the display panel is electrically connected to theflexible printed circuit in the second region, and wherein the flexibleprinted circuit is provided on a rear surface of the display panel, andwherein a display region of the display panel is located outside thehousing.
 2. The electronic device according to claim 1, wherein thedisplay panel covers the flat surface of the housing.
 3. The electronicdevice according to claim 1, wherein each of the second side surface andthe third side surface includes a curved surface.
 4. An electronicdevice comprising: a housing; and a display panel, wherein the housingincludes a flat surface, a first side surface, second and third sidesurfaces adjacent to the first side surface and including a curvedsurface, and a fourth side surface opposite to the first side surface,wherein the display panel includes a first region overlapping with theflat surface, a second region overlapping with the first side surfaceand including a curved surface, a third region overlapping with thesecond side surface and including a curved surface, and a fourth regionoverlapping with the third side surface and including a curved surface,wherein a corner portion formed by the first side surface and the secondside surface included in the housing and a corner portion formed by thefirst side surface and the third side surface included in the housingare provided at a position not overlapping with the display panel, andwherein a display region of the display panel is located outside thehousing.
 5. The electronic device according to claim 4, wherein thedisplay panel covers the flat surface of the housing.
 6. The electronicdevice according to claim 4, wherein each of the first side surface andthe fourth side surface includes a curved surface.
 7. An electronicdevice comprising: a housing; a display panel including a flexiblesubstrate; and a flexible printed circuit, wherein the housing includes:a flat surface including two long sides and two short sides; a firstside surface extending from one of the two long sides and including acurved surface region; a second side surface extending from one of thetwo short sides; a third side surface extending from the other of thetwo short sides; and a fourth side surface extending from the other ofthe two long sides and including a curved surface region, wherein theflexible substrate includes: a first side; a second side adjacent to thefirst side and overlapping with the first side surface; a third sideadjacent to the first side and overlapping with the fourth side surface;a fourth side opposite to the first side, and a protruding portionextending from the first side so as to be bendable and including aregion overlapping with the flexible printed circuit, and wherein adisplay region of the display panel is located outside the housing. 8.The electronic device according to claim 7, wherein the display panelcovers the flat surface of the housing.
 9. An electronic devicecomprising: a housing; a display panel including a flexible substrate;and a flexible printed circuit, wherein the housing includes: a flatsurface including two long sides and two short sides; a first sidesurface extending from one of the two long sides and including a curvedsurface region; a second side surface extending from one of the twoshort sides; a third side surface extending from the other of the twoshort sides; and a fourth side surface extending from the other of thetwo long sides and including a curved surface region, wherein theflexible substrate includes: a first side; a second side adjacent to thefirst side and overlapping with the first side surface; a third sideadjacent to the first side and overlapping with the fourth side surface;a linear fourth side opposite to the first side, and a protrudingportion extending from the first side so as to be bendable and includinga region overlapping with the flexible printed circuit, and wherein adisplay region of the display panel is located outside the housing. 10.The electronic device according to claim 9, wherein the display panelcovers the flat surface of the housing.